Field of the Invention
The invention relates to a code signal generator, in particular for an anti-theft protection system of a motor vehicle.
A prior art code signal generator (European Patent Application EP 0 659 963 A1) has a transponder unit, which receives a question code signal from a transmitting and receiving (transceiver) unit disposed in the motor vehicle. In response, a response code signal is generated in the code signal generator with the aid of the question code signal and transmitted back to the transmitting and receiving unit in the motor vehicle. In the event of authorization of the response code signal (authentication) an immobilizer of the motor vehicle is released.
In addition, the code signal generator has a remote control unit, which is independent of the transponder unit, generates a coded control signal after the actuation of a pushbutton switch and transmits the signal via an antenna. A receiving unit in the motor vehicle receives the coded control signal and controls the central locking system if the control signal is authorized.
In this case, the transponder unit and the remote control unit are arranged independently of one another on a key grip. Each unit has a computing unit which respectively generates is the response code signal and the control signal.
A further known code signal generator (International Application WO 96/17290) has either a transponder unit or a remote control unit. Only the remote control unit is required in the event of unidirectional signal transmission, and only the transponder unit in the event of bidirectional signal transmission. To make it more difficult to intercept the transmitted signals, the same signal is transmitted via at least two different transmission channels. The code signal generator therefore has two different transmitters. The two received signals must be correct in order to enable a security unit to be controlled.